Technical Field
The present invention relates generally to consumer and commercial appliances, and more particularly to consumer and commercial clothes dryers. This invention relates to clothes dryers having an improved output exhaust duct.
Background
Clothes dryers are a leading cause of residential fires in the United States. In 2010, clothes dryers and washing machines accounted for 4.5% of all reported home structure fires, 1.9% of associated civilian deaths, 2.8% of associated civilian injuries, and 3.1% of associated direct property damage. Clothes dryers accounted for 92% of these fires; washing machines 4%, and washer and dryer combinations accounted for 4%. The risk of fire is roughly equal for gas and electric dryers.
From 2006-2010, the National Fire Protection Association NFPA reported a yearly average of over 15 thousand dryer fires in the United States per year, resulting in a yearly average of 29 deaths, 402 injuries and approximately $192 million in direct property damage. The leading cause of home clothes dryer and washer fires was failure to clean 32%, followed by unclassified mechanical failure or malfunction 22%. Eight percent were caused by some type of electrical failure or malfunction. Out of these fires, the leading item first ignited in a clothes dryer fire was dust, fiber, or lint, causing 29% of the fires and 85% of the deaths.
Many fires are caused each year by ignition of the flexible exhaust ducting that carries lint and exhaust air from the clothes dryer exhaust outlet to a vent system that is part of the residence. Should the dryer chassis become inadvertently energized, the fault current is seen to flow through the “spring” (i.e., a coiled steel helix) that is part of the flexible exhaust duct. The steel, which is not a good conductor of electricity, will overheat and cause the plastic to melt and or ignite, as well as the internal lint to smolder and/or ignite. The exhaust duct is often made of a polymer, but sometimes made of aluminum foil that is very thin. In either case, energization of the steel or the foil can bring about this heating and/or arc production because of poor mating of the flexible exhaust duct and the dryer exhaust flange. In the alternative, the arcing can also occur between the flexible vent tubing and vent connection that is part of the residence.
The dryer has this exhaust duct output, whether of gas fired or electrical resistance heating design. While energization by AC current has been described, the same phenomenon has also occurred when the dryer chassis is energized by lightning.
There exists, therefore, a need in the art for a clothes dryer duct connection that will prevent an electrical current from traversing the ducting and/or its conductive steel helical spring, allowing this electrical charge to overheat or melt the ducting, igniting flammable materials such as lint. There also exists a need in the art for a duct connection that will prevent an electrical current from arcing between the ducting and the dryer or wall, thus igniting the flammable materials within or attached to the duct.